Method for producing group III element nitride single crystal and group III element nitride transparent single crystal prepared thereby

ABSTRACT

A method for producing a Group III element nitride single crystal, which comprises reacting at least one Group III element selected from the group consisting of gallium(Ga), aluminum(Al) and indium(In) with nitrogen(N) in a mixed flux of sodium(Na) and at least one of an alkali metal (except Na) and an alkaline earth metal. The method allows the production, with a good yield, of the single crystal of a group III element nitride which is transparent, is reduced in the density of dislocation, has a bulk form, and is large. In particular, a gallium nitride single crystal produced by the method has high quality and takes a large and transparent bulk form, and thus has a high practical value.

TECHNICAL FIELD

The present invention relates generally to a method for producing singlecrystal of a Group-III-element nitride.

BACKGROUND ART

Group-III-element nitride semiconductors have been used in the field ofheterojunction high-speed electron devices or photoelectron devices(semiconductor lasers, light emitting diodes, sensors, etc.), forexample. Among the Group-III-element nitride semiconductors, galliumnitride (GaN) in particular has been gaining attention. Heretofore,gallium nitride single crystal has been obtained by reacting galliumwith nitrogen gas directly (J. Phys. Chem. Solids, 1995, 56, 639). Inthis case, however, an extremely high temperature of 1300° C. to 1600°C. and an extremely high pressure of 8000 to 17000 atm (about 800 toabout 1700 MPa) are required. In order to solve this problem, atechnique for growing gallium nitride single crystal in a sodium (Na)flux (hereinafter such a technique also is referred to as a “Na fluxmethod”) has been developed (e.g., U.S. Pat. No. 5,868,837). Accordingto this method, it is possible to reduce the required heatingtemperature drastically to 600° C. to 800° C. and also the requiredpressure to about 50 atm (about 5 MPa). However, the single crystalobtained by this method is blackened, thereby posing a problem inquality. Furthermore, although the temperature and pressure required bythis method are much lower than those required when producing the singlecrystal by reacting gallium with nitrogen gas directly, the conditionsrequired by this method are still stringent, and there are demands forfurther reduction, especially in the required pressure. Moreover,conventional techniques cannot produce bulk-sized large transparentgallium nitride single crystal that has a low dislocation density and isof high quality. Besides, the conventional techniques can achieve only apoor yield. More specifically, according to the conventional techniques,the growth rate of the single crystal is extremely slow, for example,about a few micrometers per hour. Thus, even when gallium nitride isgrown for 1000 hours, the size of the obtained single crystal is onlyabout a few millimeters. In fact, the largest gallium nitride singlecrystal that has ever been reported had a maximum diameter of only about1 cm. Thus, it has been difficult to put gallium nitride to practicaluse. A method for growing gallium nitride single crystal by reactinglithium nitride (Li₃N) with gallium also has been reported (Journal ofCrystal Growth 247 (2003) 275-278), for example. However, according tothis method, the size of the obtained crystal is only about 1 to 4 mm.The above-described problems are not specific to gallium nitride, butmay occur in other Group-III-element nitride semiconductors.

DISCLOSURE OF INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide a method for producing bulk-sized large transparentGroup-III-element nitride single crystal that has a low dislocationdensity and is of high quality with a high yield.

In order to achieve the above object, a first method for producingGroup-III-element nitride single crystal according to the presentinvention includes: reacting at least one Group III element selectedfrom the group consisting of gallium (Ga), aluminum (Al), and indium(In) with nitrogen (N) in a mixed flux containing sodium (Na) and atleast one of an alkali metal (other than Na) and an alkaline-earthmetal, thereby causing Group-III-element nitride single crystal to grow.

By reacting the Group III element such as gallium with nitrogen in themixed flux containing sodium and at least one of an alkali metal (otherthan Na) and an alkaline-earth metal as described above, it is possibleto produce bulk-sized large transparent single crystal that has a lowdislocation density and is of high quality. Moreover, the pressure to beapplied during the reaction may be lower than that in the conventionaltechniques. The above-noted U.S. patent Publication describes the use ofa flux containing sodium alone and the use of an alkaline-earth metal asa catalyst. However, it is to be noted here that the above-describedfirst production method uses the mixed flux containing sodium (Na) andat least one of an alkali metal (other than Na) and an alkaline-earthmetal, and the alkaline-earth metal is not used as a catalyst. This is asignificant difference between the first production method and the aboveU.S. patent Publication. Owing to this difference, the first productionmethod can produce bulk-sized large transparent Group-III-elementnitride single crystal that is of high quality.

A second production method according to the present invention includes:reacting at least one Group III element selected from the groupconsisting of gallium (Ga), aluminum (Al), and indium (In) with nitrogen(N) in a metal flux containing at least one of an alkali metal and analkaline-earth metal, thereby causing Group-III-element nitride singlecrystal to grow. In the second production method, a Group-III-elementnitride is provided beforehand, and the Group-III-element nitride isbrought into contact with the metal flux to cause new Group-III-elementnitride single crystal to grow using the Group-III-element nitride as anucleus.

The second production method also can produce bulk-sized largetransparent Group-III-element nitride single crystal that is of highquality. Moreover, according to this method, the conditions required forthe reaction can be made less stringent than in conventional techniques.Note here that the most important feature of the second productionmethod is that it can produce large single crystal quickly. That is, inthe second production method, as the size of the Group-III-elementnitride serving as a nucleus increases, larger Group-III-element nitridesingle crystal can be obtained more quickly. For example, when galliumnitride that is in the form of a thin film is used as a nucleus, galliumnitride single crystal having the same area as the thin film grows inthe thickness direction. Thus, for example, in the case where the thinfilm having a maximum diameter of 5 cm is used, when gallium nitridesingle crystal having the same area as the thin film grows in thethickness direction by several micrometers to several millimeters,sufficiently large bulk-sized gallium nitride can be obtained. The sameapplies to other Group-III-element nitrides.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are schematic views showing the configuration of anexample of an apparatus to be used for producing gallium nitride singlecrystal.

FIG. 2 shows scanning electron microscope (SEM) photographs of galliumnitride single crystal obtained by an example of a production methodaccording to the present invention.

FIGS. 3A and 3B are scanning electron microscope (SEM) photographs ofgallium nitride single crystal obtained by another example of aproduction method according to the present invention. FIG. 3A is the SEMphotograph at 500× magnification, and FIG. 3B is the SEM photograph at6000× magnification.

FIG. 4 is an optical microscope photograph (245× magnification) ofgallium nitride single crystal obtained by still another example of aproduction method according to the present invention.

FIG. 5 is a graph showing a relationship between a pressure during thereaction and a yield of gallium nitride single crystal in still anotherexample of a production method according to the present invention.

FIG. 6 is an optical microscope photograph (245× magnification) ofgallium nitride single crystal obtained by still another example of aproduction method according to the present invention.

FIG. 7 is a photograph of gallium nitride single crystal obtained bystill another example of a production method according to the presentinvention.

FIG. 8 is a graph showing a photoluminescence intensity in still anotherexample of the present invention.

FIGS. 9A and 9B are scanning electron microscope (SEM) photographs ofgallium nitride single crystal obtained by still another example of aproduction method according to the present invention. FIG. 9A is the SEMphotograph at 1000× magnification, and FIG. 9B is the SEM photograph at130× magnification.

FIG. 10 is a scanning electron microscope (SEM) photograph (7000×magnification) of gallium nitride single crystal obtained by stillanother example of a production method according to the presentinvention.

FIG. 11 is a cross-sectional view showing an example of a field-effecttransistor according to the present invention.

FIG. 12 is a cross-sectional view showing an example of an LED accordingto the present invention.

FIG. 13 is a cross-sectional view showing an example of an LD accordingto the present invention.

FIG. 14 is a cross-sectional view showing an example of a semiconductorsensor according to the present invention.

FIG. 15 is graphs showing the results of PL measurement performed withrespect to GaN single crystals obtained by still another example of aproduction method according to the present invention.

FIG. 16A is a graph showing background of SIMS analysis, and FIG. 16B isa graph showing the result of SIMS analysis performed with respect tothe GaN single crystal obtained in the example shown in FIG. 15.

FIG. 17 is a graph showing a relationship between a ratio of Ca in aNa—Ca mixed flux and a yield of GaN single crystal in still anotherexample of a production method according to the present invention.

FIG. 18 is a TEM photograph showing a cross section of a GaN singlecrystal thin film produced by MOVPE in still another example of aproduction method according to the present invention.

FIG. 19 shows the result of PL measurement performed with respect to theGaN single crystal thin film produced by MOVPE in the example shown inFIG. 18.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described more specificallyby way of examples.

In the present invention, the Group III element may be gallium (Ga),aluminum (Al), and indium (In). Among them, gallium is preferred.Furthermore, the Group-III-element nitride single crystal preferably isgallium nitride (GaN) single crystal. The conditions described in thefollowing are favorable especially for producing gallium nitride singlecrystal. However, they are applicable to the production of singlecrystal of other Group-III-element nitrides as well.

In the first production method of the present invention, examples of thealkali metal include lithium (Li), potassium (K), rubidium (Rb), cesium(Cs), and francium (Fr), and examples of the alkaline-earth metalinclude calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Theymay be used individually or two or more of them may be used together.Among them, Li, Ca, K, Rb, and Cs are preferable, and Li and Ca are morepreferable. The alkali metal (other than Na) and/or the alkaline-earthmetal may be added so that the ratio (mol %) thereof to the total of thesodium (Na) and the alkali metal (other than Na) and/or thealkaline-earth metal is, for instance, in the range from 0.1 to 99 mol%, preferably from 0.1 to 50 mol %, more preferably from 0.1 to 35 mol%, and still more preferably from 0.1 to 30 mol %. Furthermore, in thecase where calcium (Ca) alone is used, the ratio (mol %) of the calcium(Ca) to the total of the sodium (Na) and the calcium (Ca) is, forinstance, in the range from 0.1 to 99 mol %, preferably from 0.1 to 50mol %, more preferably from 0.1 to 35 mol %, and still more preferablyfrom 0.1 to 30 mol %. Also, the ratio (mol %) of the sodium (Na) to thetotal of the gallium (Ga) and the sodium (Na) is, for instance, in therange from 0.1 to 99.9 mol %, preferably from 30 to 99 mol %, and morepreferably from 60 to 95 mol %. The mole ratio of the gallium, sodium,and calcium particularly preferably is Ga:Na:Ca=3.7:9.75:0.25 or27:51:22. However, note here that the present invention is not limitedto the above-mentioned ranges.

In the first production method of the present invention, the melting canbe carried out, for example, under conditions of a temperature of 100°C. to 1500° C. and a pressure of 100 Pa to 200 MPa; preferably atemperature of 300° C. to 1200° C. and a pressure of 0.01 MPa to 50 MPa;and more preferably a temperature of 500° C. to 1100° C. and a pressureof 0.1 MPa to 6 MPa.

In the first production method of the present invention, the nitrogen(N) containing gas may be, for example, nitrogen (N₂) gas, ammonia (NH₃)gas, or the like. Alternatively, the nitrogen (N) containing gas may bea mixed gas obtained by mixing these gases, and the mixing ratio thereofis not particularly limited. Above all, ammonia gas is preferablebecause the pressure required during the reaction can be reduced.

The first production method of the present invention may be used incombination with the second production method. More specifically, aGroup-III-element nitride such as gallium nitride may be providedbeforehand, and then the Group-III-element nitride may be brought intocontact with the mixed flux to cause new Group-III-element nitridesingle crystal to grow using the Group-III-element nitride as a nucleus.The conditions and the like required in this case are the same as thosein the second production method to be described later.

In the first production method, the mixed flux may contain an impurityas a dopant. By so doing, it is possible to produce gallium nitridesingle crystal containing an impurity. Examples of the impurity includecarbon (C), oxygen (O), silicon (Si), alumina (Al₂O₃), indium (In),aluminum (Al), indium nitride (InN), silicon oxide (SiO₂), indium oxide(In₂O₃), zinc (Zn), magnesium (Mg), zinc oxide (ZnO), magnesium oxide(MgO), and germanium (Ge).

The first production method according to the present invention can becarried out, for example, by using an apparatus shown in FIG. 1. Asshown in FIG. 1A, the apparatus includes a gas cylinder 1, an electricfurnace 4, and a pressure- and heat-resistant container 3 disposed inthe electric furnace 4. To the gas cylinder 1, a pipe 21 is connected.The pipe 21 is provided with a gas pressure regulator 5 and a pressureregulating valve 25, and a leak pipe having a leak valve 24 on its endis connected to a certain position of the pipe 21 excluding both endsthereof. The pipe 21 is connected to a pipe 22, and the pipe 22 isconnected to a pipe 23. The pipe 23 extends into an inner space of theelectric furnace 4 and is connected to the pressure- and heat-resistantcontainer 3. Furthermore, as shown in FIG. 1B, a crucible 6 is disposedin the pressure- and heat-resistant container 3. The crucible 6 containsgallium, sodium, and either one of or both an alkali metal (other thanNa) and an alkaline-earth metal. As the crucible, a BN crucible can beused, for example.

The method for producing Group-III-element nitride single crystal usingthis apparatus is carried out in the following manner, for example.First, materials such as a Group III element (e.g., gallium), sodium,and calcium are put in the crucible 6, and then the crucible 6 isdisposed in the pressure- and heat-resistant container 3. Thereafter,the pressure- and heat-resistant container 3 is disposed in the electricfurnace 4 with the end of the pipe 23 being connected to the pressure-and heat-resistant container 3. In this state, nitrogen-containing gasis supplied from the gas cylinder 1 to the pressure- and heat-resistantcontainer 3 through the pipes (21, 22, 23) and the pressure- andheat-resistant container 3 is heated by the electric furnace 4. Thepressure inside the pressure- and heat-resistant container 3 isregulated by the pressure regulator 5. The materials in the crucible 6are melted by being pressurized and heated for a certain period so as togrow single crystal of a Group-III-element nitride such as galliumnitride. Thereafter, the thus-obtained single crystal is taken out ofthe crucible.

Next, as described above, the second production method according to thepresent invention is a method for producing Group-III-element nitridesingle crystal, including: reacting at least one Group III elementselected from the group consisting of gallium (Ga), aluminum (Al), andindium (In) with nitrogen (N) in a metal flux containing at least one ofan alkali metal and an alkaline-earth metal, thereby causingGroup-III-element nitride single crystal to grow, wherein aGroup-III-element nitride is provided beforehand, and theGroup-III-element nitride is brought into contact with the metal flux tocause new Group-III-element nitride single crystal to grow using theGroup-III-element nitride as a nucleus.

The Group-III-element nitride that serves as a nucleus may be singlecrystal, polycrystal, or amorphous, but preferably is either singlecrystal or amorphous. The nucleus may be in any form, but preferably isin the form of a substrate or a thin film. When the nucleus is in theform of a thin film, the thin film may be formed on a substrate.Examples of a material for the substrate include amorphous galliumnitride (GaN), amorphous aluminum nitride (AlN), sapphire, silicon (Si),gallium arsenide (GaAs), gallium nitride (GaN), aluminum nitride (AlN),silicon carbide (SiC), boron nitride (BN), lithium gallium oxide(LiGaO₂), zirconium boride (ZrB₂), zinc oxide (ZnO), various types ofglass, various types of metal, boron phosphide (BP), MoS₂, LaAlO₃, NbN,MnFe₂O₄, ZnFe₂O₄, ZrN, TiN, gallium phosphide (GaP), MgAl₂O₄, NdGaO₃,LiAlO₂, ScAlMgO₄, and Ca₈La₂(PO₄)₆O₂. The thickness of the nucleus thatis in the form of a thin film is not particularly limited, and may be,for instance, in the range from 0.0005 to 100000 μm, preferably from0.001 to 50000 μm, and more preferably from 0.01 to 5000 μm. The nucleusin the form of a thin film can be formed on a substrate by, for example,metal organic chemical vapor deposition (MOCVD), hydride vapor phaseepitaxy (HVPE), or molecular beam epitaxy (MBE). Note here that asubstrate on which a gallium nitride thin film is formed is commerciallyavailable and may be used in the present invention. Furthermore, asdescribed above, a substrate itself may be used as a nucleus. Themaximum diameter of the thin film or the substrate may be, for example,at least 2 cm, preferably at least 3 cm, more preferably at least 4 cm,and still more preferably at least 5 cm. Note here that a larger maximumdiameter is preferred, and there is no upper limit of the maximumdiameter. In view of the fact that the standard for a bulk compoundsemiconductor is 2 inches, the maximum diameter preferably is 5 cm. Inthis case, the maximum diameter may be in the range from, for example, 2to 5 cm, preferably 3 to 5 cm, more preferably 4 to 5 cm, and mostsuitably 5 cm. The maximum diameter as used herein is the longest linethat joins two points on the perimeter of the thin film surface or thesubstrate surface.

In this production method, there is a possibility that theGroup-III-element nitride (nucleaus) such as gallium nitride that hasbeen provided beforehand may be dissolved in the flux before theconcentration of the nitrogen increases. In order to prevent this, it ispreferable that a nitride is present in the flux at least at an initialstage of the reaction. Examples of the nitride include Ca₃N₂, Li₃N,NaN₃, BN, Si₃N₄, and InN. They may be used individually or two or moreof them may be used together. Furthermore, the ratio of the nitride inthe flux may be, for example, 0.0001 mol % to 99 mol %, preferably 0.001mol % to 50 mol %, and more preferably 0.005 mol % to 5 mol %. Also inthe first production method, it is preferable that a nitride is presentin the flux in order to prevent the dissolution of the Group-III-elementnitride such as gallium nitride serving as a nucleus, and conditionssuch as a type and a ratio of the nitride are the same as those in thesecond production method.

In the second production method, the flux may contain an impurity as inthe case of the first production method, and the type or the like of theimpurity may be the same as that described above.

In the second production method of the present invention, examples ofthe alkali metal include lithium (Li), sodium (Na), potassium (K),rubidium (Rb), cesium (Cs) and francium (Fr), and examples of thealkaline-earth metal include calcium (Ca), strontium (Sr), barium (Ba),and radium (Ra). They may be used individually (a single-substance flux)or two or more of them may be used together (a mixed flux). As in thecase of the first production method, a mixed flux containing sodium andone or more other metals may also be used in the second productionmethod. The type, conditions, etc. of the mixed flux are the same asthose described above.

The second production method can be carried out in the same manner asthat for carrying out the first production method, except that aGroup-III-element nitride is provided beforehand and theGroup-III-element nitride is brought into contact with the flux. Forexample, in the apparatus shown in FIG. 1, a substrate on which a thinfilm of a Group-III-element nitride such as gallium nitride is formedmay be placed in the crucible, so that the Group-III-element nitridereacts with nitrogen in the flux.

Group-III-element nitride transparent single crystal of the presentinvention can be obtained in the manners described above. However, amethod other than those described above also may be used to produce thesingle crystal of the present invention. The Group-III-element nitridetransparent single crystal according to the present invention isbulk-sized transparent Group-III-element nitride single crystal having adislocation density of 10⁵/cm² or less and a maximum diameter of atleast 2 cm. The dislocation density of the single crystal according tothe present invention preferably is 10⁴/cm² or less, more preferably10³/cm² or less, and still more preferably 10²/cm² or less. Mostsuitably, the single crystal according to the present invention has anegligible dislocation density (e.g., 10¹/cm² or less). Furthermore, themaximum diameter of the single crystal according to the presentinvention may be, for example, at least 2 cm, preferably at least 3 cm,more preferably at least 4 cm, and still more preferably at least 5 cm.Note here that a larger maximum diameter is preferred, and there is noupper limit of the maximum diameter. In view of the fact that thestandard for a bulk compound semiconductor is 2 inches, the maximumdiameter preferably is 5 cm. In this case, the maximum diameter may bein the range from, for example, 2 to 5 cm, preferably 3 to 5 cm, morepreferably 4 to 5 cm, and most suitably 5 cm. The maximum diameter asused herein is the longest line that joins two points on the perimeterof the single crystal. As described in the following examples, GaNsingle crystal as one of the Group-III-element nitride single crystalsof the present invention does not contain Na as an impurity, and anelectrical resistance thereof can be made high (i.e., the GaN singlecrystal can exhibit a semi-insulating property or an insulatingproperty). Furthermore, the GaN single crystal can exhibit excellentelectroconductivity when doped with impurities. Moreover, the GaN singlecrystal of the present invention can exhibit high photoluminescence (PL)intensity. Besides, the GaN single crystal is advantageous in that itallows a GaN single crystal thin film formed thereon by MOVPE or thelike to be of high quality.

Next, a semiconductor device that uses Group-III-element nitridetransparent single crystal of the present invention will be described byway of examples. Although the following examples are directed to afield-effect transistor, a light emitting diode (LED), a semiconductorlaser diode (LD), and an optical sensor, the semiconductor device of thepresent invention is not limited thereto. Further examples of thesemiconductor device that uses the single crystal of the presentinvention include the following: a semiconductor device having a simplestructure with p-type and n-type semiconductors merely being joined toeach other, which uses the single crystal of the present invention as atleast one of the semiconductors (e.g., a pnp-type transistor, annpn-type transistor, or an npnp-type thyristor); and a semiconductordevice that uses the single crystal of the present invention as aconductive layer, substrate, or semiconductor or as an insulating layer,substrate, or semiconductor. The semiconductor device of the presentinvention can be produced by using the production method of the presentinvention in combination with a conventional method. For example, a GaNsubstrate may be produced by the production method of the presentinvention, and a semiconductor layer may be formed on the thus-obtainedsubstrate by MOCVD or the like. A GaN thin film or the like that isgrown by MOCVD or the like on a GaN substrate produced by the productionmethod of the present invention are of high quality and thus can exhibitexcellent properties. Moreover, the production method of the presentinvention also can be used to form a semiconductor layer. Specifically,first, predetermined materials are put in a crucible to form an n-typeGaN layer in a nitrogen containing gas atmosphere by the productionmethod of the present invention. Then, a p-type GaN layer is formed onthe n-type GaN layer in the same manner as in the above except that thematerials are changed. In this manner, it is possible to produce a pnjunction semiconductor device. This method also can be applied to theproduction of a field-effect transistor, an LED, an LD, a semiconductoroptical sensor, and other semiconductor devices, which will be describedlater. However, it is to be noted here that the method for producing thesemiconductor device of the present invention is not limited to themethods described above, and can be produced by any other methods.

FIG. 11 shows an example of a field-effect transistor that usesGroup-III-element nitride transparent single crystal according to thepresent invention. As shown in FIG. 11, in this field-effect transistor30, a conductive semiconductor layer 32 is formed on an insulatingsemiconductor layer 31, and a source electrode 33, a gate electrode 34,and a drain electrode 35 are formed on the conductive semiconductorlayer 32. In FIG. 11, reference numeral 37 denotes high-concentrationtwo-dimensional electrons. In this field-effect transistor, at least oneof a substrate for growing the insulating semiconductor layer 31, theinsulating semiconductor layer 31, and the conductive semiconductorlayer 32 is formed of Group-III-element nitride transparent singlecrystal of the present invention. The transparent single crystal of thepresent invention has fewer defects and is excellent in asemi-insulating property or an insulating property as long as it is notdoped with impurities. Thus, the insulating semiconductor layer 31 maybe formed of the single crystal according to the present invention. Forexample, although GaN single crystal theoretically has an excellent highfrequency property, it has been difficult to realize a field-effecttransistor with an excellent high frequency property using conventionalGaN single crystal due to the defects of the GaN single crystal. Incontrast, the GaN single crystal according to the present invention hassubstantially no dislocations and is of high quality. Hence, by usingthe GaN single crystal of the present, it is possible to obtain afield-effect transistor having an excellent high frequency property asexpected.

A field-effect transistor of the present invention may include asubstrate, on which the field-effect transistor element as describedabove may be provided. In this case, the substrate may be formed ofGroup-III-element nitride transparent single crystal according to thepresent invention. Alternatively, the substrate may be a SiC substrate,an AlN substrate, or a substrate formed of other materials such assapphire.

Next, a light emitting diode (LED) that uses the single crystal of thepresent invention includes an n-type semiconductor layer, an activeregion layer, and a p-type semiconductor layer that are laminated inthis order, and at least one of these three layers is formed ofGroup-III-element nitride transparent single crystal of the presentinvention. The n-type or p-type semiconductor can be obtained byproducing single crystal doped with an appropriate impurity according tothe production method of the present invention. FIG. 12 shows an exampleof an LED according to the present invention. As shown in FIG. 12, in anLED 40, an InGaN layer 42 as an active layer is formed between an n-typeGaN layer 41 and a p-type GaN layer 43. Furthermore, an n electrode 44is disposed on the n-type GaN layer 41 while a p electrode 45 isdisposed on the p-type GaN layer 43, which allows the LED to be compact.In contrast, conventional LEDs cannot achieve a compact structurebecause a substrate is formed of an insulating material, which requiresan n-type semiconductor layer to be formed in an L-shape so that an nelectrode is formed on a portion of the n-type semiconductor layer thatsticks out the side.

An LED of the present invention may include a substrate, on which thelight emitting diode element as described above may be provided. In thiscase, the substrate may be formed of the Group-III-element nitridetransparent single crystal of the present invention. Alternatively, thesubstrate may be a SiC substrate, an AlN substrate, or a substrateformed of other materials such as sapphire. However, when the substrateis formed of the single crystal according to the present invention, thesubstrate can be conductive, which allows an electrode to be disposedunder the substrate.

In the LED of the present invention, the p-type semiconductor layer, theactive region layer, and the n-type semiconductor layer may have eithera single layer structure or a layered structure. For example, in thesemiconductor device shown in FIG. 12, a laminate of a p-type AlGaNlayer and a p-type GaN layer may be provided instead of the p-type GaNlayer 43.

Next, a semiconductor laser diode (LD) that uses the single crystal ofthe present invention includes an n-type semiconductor layer, an activeregion layer, and a p-type semiconductor layer that are laminated inthis order, and at least one of these three layers is formed ofGroup-III-element nitride transparent single crystal of the presentinvention. Such an example is shown in FIG. 13. As shown in the drawing,in an LD 50, an InGaN layer 52 as an active layer is formed between ann-type GaN layer 51 and a p-type GaN layer 53. Furthermore, an nelectrode 54 is disposed on the n-type GaN layer 51 while a p electrode55 is disposed on the p-type GaN layer 53, which allows the LD to becompact. In contrast, conventional LDs cannot achieve a compactstructure because a substrate is formed of an insulating material, whichrequires an n-type semiconductor layer to be formed in an L-shape sothat an n electrode is formed on a portion of the n-type semiconductorlayer that sticks out the side.

An LD of the present invention may include a substrate, on which thesemiconductor laser diode element as described above may be provided. Inthis case, the substrate may be formed of the Group-III-element nitridetransparent single crystal of the present invention. Alternatively, thesubstrate may be a SiC substrate, an AlN substrate, or a substrateformed of other materials such as sapphire. However, when the substrateis formed of the single crystal according to the present invention, thesubstrate can be conductive, which allows an electrode to be disposedunder the substrate.

In the LD of the present invention, the p-type semiconductor layer, theactive region layer, and the n-type semiconductor layer may have eithera single layer structure or a layered structure. For example, in thesemiconductor device shown in FIG. 13, a laminate in which a p-typeAlGaN capping layer, a p-type GaN waveguiding layer, a p-type AlGaN/GaNMD-SLS cladding layer, and a p-type GaN layer are laminated in thisorder may be provided instead of the p-type GaN layer 53, and a laminatein which an n-type AlGaN/GaN MD-SLS cladding layer and an n-type GaNwaveguiding layer are laminated in this order may be formed instead ofthe n-type GaN layer.

Next, a semiconductor optical sensor according to the present inventionis an optical sensor element in which a p-type semiconductor layer andan n-type semiconductor layer are joined to each other, and at least oneof the semiconductor layers is formed of the Group-III-element nitridetransparent single crystal according to the present invention. FIG. 14shows an example of such a semiconductor optical sensor. As shown inFIG. 14, a semiconductor optical sensor 60 includes a GaN substrate 65having three projections. An n-type GaN layer 61 and a p-type GaN layer62 are laminated in this order on each of the projections, and at leastone of these layers is formed of single crystal according to the presentinvention. An n electrode 64 (Au/Ti electrode) is formed on the bottomof the substrate 65, while a p electrode 63 (Au/Ti electrode) is formedon the p-type GaN layer 62 on each of the projections.

A semiconductor optical sensor of the present invention may include asubstrate, on which the semiconductor optical sensor as described abovemay be provided. In this case, the substrate may be formed of theGroup-III-element nitride transparent single crystal of the presentinvention. Alternatively, the substrate may be a SiC substrate, an AlNsubstrate, or a substrate formed of other materials such as sapphire.However, when the substrate is formed of the single crystal according tothe present invention, the substrate can be conductive, which allows anelectrode to be disposed under the substrate.

EXAMPLES

Hereinafter, examples of the present invention will be described alongwith comparative examples.

Example 1

Using the apparatus shown in FIG. 1, single crystal of gallium nitridewas produced in the same manner as described above. More specifically,gallium, sodium, and calcium were put in a BN crucible, and then theywere melted by being pressurized and heated under the followingconditions in a nitrogen (N₂) gas atmosphere so as to grow singlecrystal of gallium nitride. In the present example, the sodium and thecalcium were blended so as to have the following six different blendratios.

(Producing Conditions)

-   -   Growth temperature: 800° C.    -   Growth pressure (N₂): 30 atm (3.04 MPa)    -   Growth period: 96 hours    -   Crucible used: BN crucible        (Blend Ratio)

With respect to 1 g of gallium (Ga), sodium (Na) and calcium (Ca) wereblended so that they were present at the ratios indicated in thefollowing table.

Sample No. Na:Ca (mole ratio) Na (g) Ca (g) 1. 9.75:0.25 0.859560.038422 2. 9:1 0.79344 0.153688 3. 8.5:1.5 0.74936 0.230531 4. 8:20.70528 0.307375 5. 7.5:2.5 0.6612 0.384219 6. 7:3 0.61712 0.461063

With regard to each of the thus-obtained six types of single crystals(samples 1 to 6), it was confirmed that the obtained single crystal wasof gallium nitride and the amount of gallium nitride generated wasmeasured in the following manner. Also, any blackening of the singlecrystal was observed visually and with an optical microscope. Theresults are shown in the following. Furthermore, as a comparativeexample, gallium nitride single crystal was produced in the same manneras in the example (Ga:Na (weight ratio)=3:7) except that the pressurewas set to 5 MPa and no calcium was added.

(Confirmation as to Whether the Crystals Obtained were of GalliumNitride)

Elementary analysis (EDX: Energy-Dispersive X-ray spectroscopy) andphotoluminescence (PL) were performed to confirm the single crystalsobtained were of gallium nitride. The elementary analysis was carriedout by irradiation with an electron beam with an acceleration voltage 15kV while confirming the position of the sample with an electronmicroscope. The photoluminescence measurement was carried out byirradiation with a helium-cadmium laser beam at ordinary temperature.

(Measurement of the Amount of Gallium Nitride Generated)

The volume of each of the obtained single crystals was determined, whichwas then converted into an amount of the generated gallium nitride.

Amount (g) of gallium nitride Sample No. Na:Ca (mole ratio ) generatedfrom 1.00 g of Ga 1. 9.75:0.25 0.09102 2. 9:1 0.16016 3. 8.5:1.5 0.117044. 8:2 0.13543 5. 7.5:2.5 0.13827 6. 7:3 0.01699 Comp. Ex. (Na only)0.01549

As described above, in the present example, gallium nitride singlecrystals were obtained at a low pressure. Besides, the amounts of thegallium nitride generated were equivalent to or greater than thatgenerated in the comparative example in which sodium alone was used.

FIG. 2 shows photographs of the gallium nitride single crystals obtainedin the example. In FIG. 2, the two photographs located on the upper sideare photographs of the single crystal of the sample No. 1, and the twophotographs located on the lower side are photographs of the singlecrystal of the sample No. 2. In FIG. 2, the two photographs on the leftside are optical microscope photographs at 245× magnification. On theother hand, the two photographs on the right side are SEM photographs,and one on the upper side is at 6000× magnification while the one on thelower side is at 15000× magnification. As shown in FIG. 2, these singlecrystals were colorless, transparent and of high quality. Other samplesalso were colorless, transparent, and of high quality. In contrast, thesingle crystal according to the comparative example was blackened.

Example 2

Gallium nitride single crystal was produced at a growth pressure (N₂) of15 atm. In the present example, sodium (Na) and calcium (Ca) wereblended so that 0.74936 g of sodium (Na) and 0.153688 g of calcium (Ca)(Na:Ca=9:1) were present with respect to 1 g of gallium (Ga). Except forthe above, the gallium nitride single crystal was produced in the samemanner as in Example 1. As a result, the amount of the gallium nitrideobtained was 0.06902 g.

Example 3

A rectangular sapphire substrate (4 mm×15 mm with a thickness of 0.3 mm)on which a thin film (thickness: 3 μm) of gallium nitride single crystalhad been formed was provided. The substrate was placed in a BN crucible(inner diameter: 19 mm, depth: 5 mm), and gallium (Ga), sodium (Na), andcalcium (Ca) further were put in the BN crucible. The BN crucible wasthen set in the pressure-and heat-resistant container in the apparatusshown in FIG. 1. Thereafter, nitrogen gas was supplied to the container,and the container was heated so that gallium nitride single crystal wasgrown on the thin film. The conditions for the crystal growth were asfollows. FIG. 3 shows SEM photographs of the thus-obtained singlecrystal.

(Producing Conditions)

-   -   Growth temperature: 800° C.    -   Growth pressure: 30 atm (3.04 MPa)    -   Growth period: 24 hours    -   Na:Ca=9:1 (mole ratio with respect to 1 g of gallium)

In FIG. 3, FIG. 3A is a SEM photograph at 500× magnification and FIG. 3Bis the SEM photograph at 6000× magnification. As shown in FIGS. 3A and3B, the growth of the gallium nitride single crystal 11 on the sapphiresubstrate 12 was confirmed.

Example 4

Using the apparatus shown in FIG. 1, gallium nitride single crystalswere produced in the following manner. A boron nitride cruciblecontaining a raw material (1.0 g of gallium) and a flux (sodium andcalcium) was placed in a pressure-resistant stainless steel container.The stainless steel container containing the crucible was heated to agrowth temperature of 800° C., and at the same time, the pressure ofnitrogen gas was increased to 30 atm. The temperature and pressure werekept constant for 96 hours. In the present example, the calcium andsodium as components of the flux were present at the ratios indicated inthe following table. Furthermore, the composition ratio of the galliumand the flux represented by mole ratio was adjusted so as to beconsistently 3.7:10. The yield of each gallium nitride single crystalwas shown in the following table. FIG. 4 shows a SEM photograph of thesingle crystal (Na:Ca=9:1) obtained in the present example.

yield (%) of Na:Ca gallium nitride 9.75:0.25 7.58% 9.5:0.5 13.94% 9:113.34% 8.5:1.5 9.75% 8:2 11.28% 7.5:2.5 11.51% 7:3 1.41% The fluxcontained Na alone. 1.29%

As shown in the above table, gallium nitrides were obtained with highyields. Furthermore, each of the obtained gallium nitride singlecrystals was transparent as shown in FIG. 4 and had a maximum diameterof at least 2 cm. Moreover, examination by the etching method revealedthat the gallium nitride single crystals had substantially nodislocations.

Example 5

Using the apparatus shown in FIG. 1, gallium nitride single crystal wasproduced in the following manner. A boron nitride crucible containing araw material (1.0 g of gallium) and a flux (0.50 g of sodium and 0.10 gof calcium) was placed in a pressure-resistant stainless steelcontainer. The stainless steel container containing the crucible washeated to a growth temperature of 800° C., and at the same time, thepressure of nitrogen gas was increased to a predetermined atmosphericpressure. The temperature and pressure were kept constant for 96 hours.In the present example, the mole ratio of gallium and the flux was setto 3.7:10, and the ratio of the sodium and calcium was set to 9:1. As acomparative example, gallium nitride single crystal was produced in thesame manner as in the above using a flux containing sodium alone. Theresults are shown in FIG. 5.

As can be seen from FIG. 5, although the GaN crystal generation usingthe flux containing no calcium required a nitrogen pressure of 25 atm ormore, the required nitrogen pressure was reduced to 15 atm when the fluxcontaining calcium was used.

Example 6

Using the apparatus shown in FIG. 1, gallium nitride single crystalswere produced in the following manner. A boron nitride cruciblecontaining a raw material (1.0 g of gallium) and a flux (sodium andlithium) was placed in a pressure-resistant stainless steel container.The stainless steel container containing the crucible was heated to agrowth temperature of 850° C., and at the same time, the pressure ofnitrogen gas was increased to 50 atm. These temperature and pressurewere kept constant for 96 hours. In the present example, the ratio ofthe lithium and sodium as components of the flux was varied in the rangefrom 0:1 to 1:0. Furthermore, the composition ratio of the gallium andthe flux represented by the mole ratio was adjusted so as to beconsistently 3.7:10. As a result, it was found that the yield of thebulk-sized GaN crystal at a nitrogen gas pressure of 50 atm increaseddrastically by adding lithium to the flux. Furthermore, the color ofeach of the bulk-sized GaN crystals obtained was transparent as shown inthe optical microscope photograph of FIG. 6, and the maximum diameterthereof was at least 2 cm. Moreover, examination by the etching methodrevealed that the bulk-sized GaN crystals had substantially nodislocations.

Example 7

Using the apparatus shown in FIG. 1, gallium nitride single crystal wasproduced in the following manner. A boron nitride crucible containing araw material (1.00 g of gallium), a flux (0.881g of sodium), and asapphire substrate on which a 3 μm thick GaN thin film had been formedby MOCVD was placed in a pressure-resistant stainless steel container.The stainless steel container containing the crucible was heated to agrowth temperature of 800° C., and at the same time, the pressure ofnitrogen gas was increased to 50 atm. The temperature and pressure werekept constant for 96 hours. As a result, as shown in an opticalmicroscope photograph of the FIG. 7, an 800 μm thick bulk-sized GaNcrystal was grown on the GaN thin film formed by MOCVD on the substrate.With regard to the thus-obtained bulk-sized GaN crystal,photoluminescence (PL) measurement was performed. As a result, as shownin the graph of FIG. 8, the bulk-sized GaN crystal exhibited a PLintensity 43 times as high as that of the GaN thin film formed by MOCVDas a base for growing the GaN crystal. Furthermore, as a result ofdislocation density measurement by the etching method, althoughdislocation of about 10⁶/cm² was observed in the GaN thin film formed byMOCVD on the substrate, the bulk-sized GaN crystal had substantially nodislocations (see SEM photographs of FIG. 9).

Example 8

Using the apparatus shown in FIG. 1, gallium nitride single crystal wasproduced in the following manner. A boron nitride crucible containing araw material (1.00 g of gallium), a flux (0.50 g of sodium and 0.10 g ofcalcium), and a sapphire substrate on which a 3 μm thick GaN thin filmhad been formed by MOCVD was placed in a pressure-resistant stainlesssteel container. The stainless steel container containing the cruciblewas heated to a growth temperature of 800° C., and at the same time, thepressure of nitrogen gas was increased to 5 atm. The temperature andpressure were kept constant for 96 hours. As a result, a 2 μm thickbulk-sized GaN crystal that was colorless and transparent was grown onthe 3 μm thick GaN thin film formed by MOCVD on the substrate (see a SEMphotograph of FIG. 10). The gallium nitride had a maximum diameter of atleast 2 cm. Moreover, examination by the etching method revealed thatthe gallium nitride single crystal had substantially no dislocations.

Example 9

Using the apparatus shown in FIG. 1, gallium nitride single crystalswere produced in the following manner. A boron nitride cruciblecontaining a raw material (1.00 g of gallium) and a flux (0.881 g ofsodium) was placed in a pressure-resistant stainless steel container.The stainless steel container containing the crucible was heated to agrowth temperature of 800° C., and at the same time, the pressure of araw material gas was increased to a predetermined atmospheric pressure.The temperature and pressure were kept constant for 96 hours. As the rawmaterial gas, nitrogen gas containing ammonia was used. The mixing ratioof ammonia to the nitrogen gas was varied in the range from 0% to 100%.The results are shown in the following table.

gallium nitride single crystal NH₃ ratio (%) generating pressure (atm) 025 4 20 10 15 15 15 25 10 40 10 100 10

As is clear from the results shown in the above table, the use of theammonia-containing gas allowed the gallium nitride single crystals to beobtained at a lower pressure. Each of the obtained gallium nitridesingle crystals was transparent and had a maximum diameter of at least 2cm. Moreover, examination by the etching method revealed that thegallium nitride single crystals had substantially no dislocations.

Example 10

1.0 g of Ga, a flux component(s), and a sapphire substrate were put in aBN crucible. The sapphire substrate had a 3 μm thick GaN thin filmformed by MOCVD on a surface thereof. The mole ratio of Ga and the fluxwas set to Ga:flux=2.7:7.3. In the present example, two types of fluxeswere used, namely, a flux containing 97% Na and 3% Ca and a fluxcontaining 100% Na. Using the apparatus shown in FIG. 1, nitrogen gaswas supplied, and crystal growth for 96 hours was performed at apressure of 50 atm and at a heating temperature of 800° C. After thecrystal growth, residual materials were treated with ethanol and water.Thus, two types of GaN single crystals were obtained. With regard tothese single crystals, photoluminescence (PL) measurement was performed.The PL measurement was carried out by irradiating a surface of thesingle crystal with a He—Cd laser beam (with a wavelength of 325 nm)serving as a pumping beam at an output of 10 mW. The results are shownin FIG. 15. In FIG. 15, the upper graph shows the result of the PLmeasurement with regard to the GaN thin film formed on the sapphiresubstrate as a control. The graph located in the middle shows the resultof the PL measurement with regard to the GaN single crystal obtainedusing the flux containing 100% Na. The lower graph shows the result ofthe PL measurement with regard to the GaN single crystal obtained usingthe Na—Ca mixed flux. As can be seen from FIG. 15, the PL intensity ofthe GaN single crystal obtained using the flux containing 100% Na was 47times as high as that of the control, and the PL intensity of the GaNsingle crystal obtained using the Na—Ca mixed flux was 86 times as highas that of the control. Moreover, in the GaN single crystal obtainedusing the Na—Ca mixed flux, the broad peak observed between 400 nm to570 nm in the GaN single crystal obtained using the flux containing 100%Na was not confirmed. From this fact, it can be said that, although theGaN single crystal obtained using the flux containing Na alone canachieve higher quality than the conventional GaN single crystal, the GaNsingle crystal obtained using the Na—Ca mixed flux can achieve stillhigher quality.

Next, impurities contained in the GaN single crystal obtained using theNa—Ca mixed flux were examined by secondary ion mass spectrometry(SIMS). The result of SIMS was shown in the graphs of FIG. 16. In FIG.16, the left graph shows the background, and the right graph shows theresult of SIMS. As shown in FIG. 16, in this single crystal, Ca wasdetected, but no Na or K was detected. It is to be noted that, becausethe amount of the detected Ca was very small and Ca is a P-type dopant,the Ca has no effect on the quality of the GaN single crystal.

Example 11

1.0 g of Ga, a flux component (Na), a dopant (Si), and a sapphiresubstrate were put in a BN crucible. The sapphire substrate had a 3 μmthick GaN thin film formed by MOCVD on a surface thereof. The mole ratioof Ga and Na was set to Ga:Na=2.7:7.3, and the mole ratio of Ga and Siwas set to Ga:Si=100:0.1. Using the apparatus shown in FIG. 1, nitrogengas was supplied, and crystal growth for 15 hours was performed at apressure of 50 atm and at a heating temperature of 800° C. After thecrystal growth, residual materials were treated with ethanol and water.Thus, GaN single crystal doped with Si was obtained. An electricalresistance of this GaN single crystal was measured with a tester. As aresult, the electrical resistance was 150 Ω when the distance betweenelectrodes was 5 mm. Thus, it can be said that GaN single crystal dopedwith Si has an extremely low resistance. Furthermore, as a control, GaNsingle crystal was produced in the same manner as in the above exceptthat it was not doped with Si, and an electrical resistance thereof wasmeasured in the same manner as in the above. As a result, the electricalresistance was not less than 10¹⁰ Ω, and it was found that the GaNsingle crystal was substantially an insulator.

Example 12

The weight of Ga was set to 1.0 g consistently. The mole ratio of Ga toa flux was set to Ga:flux=2.7:7.3 consistently. Na and Ca as componentsof the flux were weighed so that the mole ratio of Ca to Na (Ca/Na)varied gradually from 0 to 1. The weighed materials were put in a BNcrucible. Using the apparatus shown in FIG. 1, nitrogen gas was suppliedto the BN crucible, and the BN crucible was heated and pressurized togrow GaN single crystal. Conditions for the crystal growth were asfollows: the heating temperature was 800° C.; the pressure was 15 atm,and the growth period was 96 hours. After the crystal growth, residualmaterials were treated with ethanol and water. Thus, GaN single crystalswere obtained. The relationship between the ratio of Ca and the yield ofGaN single crystal is shown in the graph of FIG. 17. In FIG. 17, thehorizontal axis represents the ratio of Ca and the vertical axisrepresents the yield of the GaN single crystal. As shown in FIG. 17, theyield of the bulk-sized GaN crystal at a nitrogen gas pressure of 15 atmreached to 29% when the ratio of the calcium in the flux was 30% (Na70%).

Example 13

On the GaN single crystal produced using the flux containing Na alone inExample 10, a GaN single crystal thin film further was formed by MOVPE.The MOVPE was carried out under the following conditions.

(Conditions for MOVPE)

-   -   Gas: Ga(CH₃)₃, NH₃, H₂    -   Growth temperature: 1100° C.    -   Growth thickness: about 2 μm

The cross section of the GaN thin film obtained by the above-describedMOVPE was examined with a transmission electron microscope (TEM). As aresult, as shown in a TEM photograph of FIG. 18, it was confirmed thatthe GaN single crystal thin film formed by the MOVPE was present on theGaN single crystal formed using the Na flux. Also, an interface betweenboth the GaN single crystals was confirmed.

Next, PL measurement was performed with regard to the GaN(MO-GaN/NF—GaN/MO-GaN) obtained as a result of the above-describedMOVPE. Conditions for the PL measurement were the same as those inExample 10. Furthermore, as controls, the PL measurement also wasperformed with regard to a GaN single crystal thin film (MO-GaN) formedby the MOVPE on the same sapphire substrate as used in the presentexample and GaN single crystal (NF—GaN/MO-GaN) formed thereon using aflux containing Na alone. The results are shown in the graph of FIG. 19.As shown in FIG. 19, the GaN single crystal (MO-GaN/NF—GaN/MO-GaN)formed by the MOVPE on the GaN single crystal (NF—GaN/MO-GaN) formedusing the Na flux exhibited a PL intensity 4 times as high as that ofthe GaN single crystal thin film (MO-GaN) formed on the sapphiresubstrate. From this result, it can be said that when GaN single crystalobtained by the method using a Na flux according to the presentinvention is used as a substrate, it is possible to form a high-qualityGaN single crystal thin film on the substrate by MOVPE.

INDUSTRIAL APPLICABILITY

As specifically described above, the gallium nitride single crystalaccording to the present invention is bulk-sized large transparentsingle crystal that is of high quality. Thus, the gallium nitride singlecrystal of the present invention has extremely high practical value.

1. A method for producing Group-III-element nitride single crystal,comprising: reacting at least one Group III element selected from thegroup consisting of gallium (Ga), aluminum (Al), and indium (In) withnitrogen (N) in a mixed flux containing sodium (Na) and at least one ofan alkali metal (other than Na) and an alkaline-earth metal, therebycausing Group-III-element nitride single crystal to grow, wherein aratio of the alkali metal (other than Na) and the alkaline-earth metalto a total of the sodium (Na), the alkali metal (other than Na), and thealkaline-earth metal is in a range from 0.1 to 30 mol %.
 2. The methodaccording to claim 1, wherein the Group III element is gallium (Ga), andthe Group-III-element nitride single crystal is gallium nitride (GaN)single crystal.
 3. The method according to claim 1, wherein the mixedflux is a mixed flux of sodium (Na) and calcium (Ca).
 4. The methodaccording to claim 1, wherein the mixed flux is a mixed flux of sodium(Na) and lithium (Li).
 5. The method according to claim 1, wherein themixed flux is a mixed flux of sodium (Na), calcium (Ca), and lithium(Li).
 6. The method according to claim 1, wherein the reaction iscarried out under conditions of a temperature of 100° C. to 1200° C. anda pressure of 100 Pa to 200 MPa.
 7. The method according to claim 1,wherein nitrogen (N) containing gas is used as a nitrogen source.
 8. Themethod according to claim 7, wherein the nitrogen (N) containing gas isat least one selected from the group consisting of nitrogen (N₂) gas,ammonia (NH₃) gas, and a mixed gas containing the nitrogen (N₂) gas andthe ammonia (NH₃) gas.
 9. The method according to claim 1, wherein thesingle crystal is transparent.
 10. The method according to claim 1,wherein a Group-III-element nitride is provided beforehand, and theGroup-III-element nitride is brought into contact with the mixed flux tocause new Group-III-element nitride single crystal to grow using theGroup-III-element nitride as a nucleus.
 11. The method according toclaim 10, wherein the the Group-III-element nitride that serves as thenucleus is single crystal or amorphous.
 12. The method according toclaim 10, wherein the Group-III-element nitride that serves as thenucleus is in a form of a thin film.
 13. The method according to claim12, wherein the thin film is formed on a substrate.
 14. The methodaccording to claim 10, wherein a nitride is present in the mixed flux atleast at an initial stage of the reaction.
 15. The method according toclaim 14, wherein the nitride is at least one selected from the groupconsisting of Ca₃N₂, Li₃N, NaN₃, BN, Si₃N₄, and InN.
 16. The methodaccording to claim 1, wherein the mixed flux contains an impurity as adopant.
 17. The method according to claim 16, wherein the impurity is atleast one selected from the group consisting of carbon (C), oxygen (O),silicon (Si), alumina (Al₂O₃), indium (In), aluminum (Al), indiumnitride (InN), silicon oxide (SiO₂), indium oxide (In₂O₃), zinc (Zn),magnesium (Mg), zinc oxide (ZnO), magnesium oxide (MgO), and germanium(Ge).
 18. Group-III-element nitride single crystal obtained by themethod according to claim 1, wherein the single crystal is transparentand has a dislocation density of 10⁵/cm² or less.
 19. Group-III-elementnitride single crystal obtained by the method according to claim 1,wherein the single crystal is transparent and has a maximum diameter ofat least 2 cm.
 20. A semiconductor device comprising a semiconductorlayer, wherein the semiconductor layer is formed of the GroupIII-element nitride transparent single crystal according to claim 18.21. The method according to claim 1, wherein the mixed flux is a mixedflux of sodium (Na) and alkali metal other than Na.
 22. The methodaccording to claim 1, wherein the mixed flux is a mixed flux of sodium(Na) and calcium (Ca), and the growth of the single crystal is performedat a pressure of 1.5 to 3 MPa.
 23. A semiconductor device comprising aGroup III-element nitride thin film that is grown by usingGroup-III-element nitride transparent single crystal according to claim18 as a substrate.
 24. The method according to claim 3, wherein sodiumand calcium are blended, so that a mole ratio of sodium to calcium is ina range of 9.75:0.25 to 7:3 with respect to 1 g of the GroupIII-element.